Simultaneous metal, sulfur and nitrogen removal using supercritical water

ABSTRACT

A process for removing metals, sulfur and nitrogen in the upgrading of hydrocarbons comprising: mixing hydrocarbons containing metals, sulfur and nitrogen with a fluid comprising water that has been heated to a temperature higher than its critical temperature in a mixing zone to form a mixture; passing the mixture to a reaction zone; reacting the mixture in the reaction zone under supercritical water conditions in the absence of externally added hydrogen for a residence time sufficient to allow upgrading reactions to occur while maintaining an effective amount of metals, derived from the hydrocarbon undergoing upgrading, in the reaction zone to catalyze the upgrading reactions; and recovering upgraded hydrocarbons having a lower concentration of metals, sulfur and nitrogen than the hydrocarbons before reaction is disclosed.

FIELD OF THE INVENTION

The present invention relates to a process for simultaneous removal ofmetals, sulfur and nitrogen from heavy oil using supercritical water.

BACKGROUND OF THE INVENTION

Heavy oil typically contains high concentration of sulfur, metals andnitrogen. Such contaminants have very negative effects on the catalystsand equipment used in many processes for further refining to producehigh value products. Hydroprocessing is currently the process of choiceto remove metal and sulfur from heavy oil. Hydrotreating processtypically takes place in a trickle bed or fixed-bed reactor usingexpensive catalyst such as Mo and requires the use, of high pressurehydrogen which becomes more and more expensive. Hydrogen-additionprocesses such as hydrotreating or hydrocracking require significantinvestments in capital and infrastructure. Hydrogen-addition processesalso have high operating costs, since hydrogen production costs arehighly sensitive to natural gas prices. Some remote heavy oil reservesmay not even have access to sufficient quantities of low-cost naturalgas to support a hydrogen plant. These hydrogen-addition processes alsogenerally require expensive catalysts and resource intensive catalysthandling techniques, including catalyst regeneration. Therefore there isa need for improved methods/processes for heavy oil treatment to removesulfur and metal.

One alternative to hydrotreating of heavy oil to remove sulfur andmetals is to use supercritical water. However, previous processes useeither catalyst or processing gas (reducing or oxidizing gas) or both toachieve simultaneous removal of sulfur and metal. Without externallysupplied catalyst or hydrogen, the contaminate removal rate was notsatisfactory.

U.S. Pat. Nos. 4,594,141; 4,483,761; 4,557,820; and 4,559,127 relate tothe upgrading of heavy hydrocarbons using supercritical water to reducesulfur, nitrogen and metals in the products The processes disclose useadded olefin or halide components.

U.S. Pat. Nos. 3,948,754; 3,948,755 and 3,960,706 relate to a processusing supercritical water for metal and sulfur removal without externalsupply of hydrogen using an externally supplied sulfur and nitrogenresistant catalyst.

U.S. Pat. No. 5,611,915 relates to a process to remove sulfur andnitrogen components using supercritical water using high pressure CO.

U.S. Patent Application 200310168381, U.S. Patent Application2005/0040081 and U.S. Patent Application 200510072137 relate to aprocess and apparatus for treating heavy oil in such a way that vanadiumcontained in heavy oil is isolated during treatment with supercriticalor subcritical water. Oxidizing agent is used to achieve metals removal.In addition, vanadium oxide scavenger is used to remove vanadium oxideformed from oxidation of vanadium by the oxidizing agent from reformedoils.

U.S. Pat. Nos. 3,989,618 and 4,005,005 relate to a process to upgradeheavy hydrocarbons using supercritical water without external supply ofH2 or catalyst.

U.S. Pat. No. 4,446,012 relates to a process of treating heavy oil toremoves metals and sulfur using sub-critical water (T=380 to 480 C andP=725 to 2175 psi) in the absence of hydrogen and catalyst.

A process according to the present invention overcomes thesedisadvantages by using supercritical water to upgrade a heavyhydrocarbon feedstock into an upgraded hydrocarbon product or syncrudewith highly desirable properties (low sulfur content, low metalscontent, lower density (higher API), lower viscosity, lower residuumcontent, etc.). The process neither requires external supply of hydrogennor must it use catalysts. Further, the process in the present Inventiondoes not produce an appreciable coke by-product.

In comparison with the traditional processes for syncrude production,advantages that may be obtained by the practice of the present inventioninclude a high liquid hydrocarbon yield; no need for externally-suppliedhydrogen; no need to provide catalyst; significant increases in APIgravity in the upgraded hydrocarbon product; significant viscosityreduction in the upgraded hydrocarbon product; and significant reductionin sulfur, metals, nitrogen, TAN, and MCR (micro-carbon residue) in theupgraded hydrocarbon product.

SUMMARY OF THE INVENTION

The present invention relates to a process for removing metals, sulfurand nitrogen in the upgrading of hydrocarbons comprising: mixinghydrocarbons containing metals, sulfur and nitrogen with a fluidcomprising water that has been heated to a temperature higher than itscritical temperature in a mixing zone to form a mixture; passing themixture to a reaction zone; reacting the mixture in the reaction zoneunder supercritical water conditions in the absence of externally addedhydrogen for a residence time sufficient to allow upgrading reactionsincluding demetalation and desulfurization to occur while maintaining aneffective amount of metals, derived from the hydrocarbon undergoingupgrading, in the reaction zone to catalyze desulfurization reactions;and recovering upgraded hydrocarbons having a lower concentration ofmetals, sulfur and nitrogen than the hydrocarbons containing metal andsulfur.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process flow diagram of an embodiment of the presentinvention.

FIG. 2 is a process flow diagram of another embodiment of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present process is related to processes described in commonlyassigned U.S. patent application Ser. Nos. 11/555,048; 11/555,130;11/555,196; and 11/555,211, all of which were filed on Oct. 31, 2006 andwhich are incorporated by reference herein. These patent applicationsrelate to various aspects of heavy oil upgrading technology usingsupercritical water. The present disclosure also relates to processesusing supercritical water to upgrade hydrocarbons.

Reactants

Water and hydrocarbons which contain metals, sulfur and nitrogencompounds, preferably heavy hydrocarbons are the two reactants employedin a process according to the present invention.

Any heavy hydrocarbon can be suitably upgraded by a process according tothe present invention. Preferred are heavy hydrocarbons having an APIgravity of less than 20°. Among the preferred heavy hydrocarbons areheavy crude oil, heavy hydrocarbons extracted from tar sands, commonlycalled tar sand bitumen, such as Athabasca tar sand bitumen obtainedfrom Canada, heavy petroleum crude oils such as Venezuelan Orinoco heavyoil belt crudes, Boscan heavy oil, heavy hydrocarbon fractions obtainedfrom crude petroleum oils particularly heavy vacuum gas oils, vacuumresiduum as well as petroleum tar, tar sands and coal tar. Otherexamples of heavy hydrocarbon feedstocks which can be used are oilshale, shale oil, and asphaltenes.

Water

Any source of water may be used in the fluid comprising water inpracticing the present invention. Sources of water include but are notlimited to drinking water, treated or untreated wastewater, river water,lake water, seawater produced water or the like.

Mixing

In accordance with the invention, the heavy hydrocarbon feed and a fluidcomprising water that has been heated to a temperature higher than itscritical temperature are contacted in a mixing zone prior to enteringthe reaction zone. In accordance with the invention, mixing may beaccomplished in many ways and is preferably accomplished by a techniquethat does not employ mechanical moving parts. Such means of mixing mayinclude, but are not limited to, use of static mixers, spray nozzles,sonic or ultrasonic agitation. The oil and water should be heated andmixed so that the combined stream will reach supercritical waterconditions in the reaction zone.

It was found that by avoiding excessive heating of the feed oil, theformation of byproduct such as solid residues is reduced significantly.In one embodiment, the heating sequence is designed so that thetemperature and pressure of the hydrocarbons and water will reachreaction conditions in a controlled manner. This will avoid excessivelocal heating of oil, which will lead to solid formation and lowerquality product. In order to achieve better performance, the oil shouldonly be heated up with sufficient water present and around thehydrocarbon molecules. This requirement can be met by mixing oil withwater before heating up.

FIG. 1 shows an embodiment of a process according to the invention.Water is heated up to supercritical conditions by Heater 1, then thesupercritical water mixed with heavy oil feed in the mixer. Thetemperature of heavy oil feed can be kept in the range of about 100° C.to 200° C. to avoid thermal cracking but still high enough to maintainreasonable pressure drop. In an embodiment in which after mixing withheavy oil, the temperature of the water-oil mixture would be lower thancritical temperature of water, Heater 2 is used to raise the temperatureof the mixture stream to above the critical temperature of water. Inthis embodiment, the heavy oil is first partially heated up by water,then the water-oil mixture is heated to supercritical conditions by thesecond heater (Heater 2). Where after mixing with heavy oil, thetemperature of the water-oil mixture is higher than the criticaltemperature of water, a second heater would not be used.

Other methods of mixing and heating sequences based on the aboveteachings may be used to accomplish these objectives as will berecognized by those skilled in the art.

Reaction Conditions

After the reactants have been mixed, they are passed into a reactionzone in which they are allowed to react under temperature and pressureconditions of supercritical water, i.e. supercritical water conditions,in the absence of externally added hydrogen, for a residence timesufficient to allow upgrading reactions to occur. The reaction ispreferably allowed to occur in the absence of externally added catalystsor promoters.

“Hydrogen” as used herein in the phrase, “in the absence of externallyadded hydrogen” means hydrogen gas. This phrase is not intended toexclude all sources of hydrogen that are available as reactants. Othermolecules such as saturated hydrocarbons may act as a hydrogen sourceduring the reaction by donating hydrogen to other unsaturatedhydrocarbons. In addition, H₂ may be formed in-situ during the reactionthrough steam reforming of hydrocarbons and water-gas-shift reaction.

The reaction zone preferably comprises a reactor, which is equipped witha means for collecting the reaction products (syncrude, water, andgases), and a section, preferably at the bottom, where any metals orsolids (the “dreg stream”) may accumulate.

Supercritical water conditions include a temperature from 374° C. (thecritical temperature of water) to 1000° C., preferably from 374° C. to600° C. and most preferably from 374° C. to 400° C., a pressure from3,205 (the critical pressure of water) to 10,000 psia, preferably from3,205 psia to 7,200 psia and most preferably from 3,205 to 4,000 psia,an oil/water volume ratio from 1:0.1 to 1:10, preferably from 1:0.5 to1:3 and most preferably about 1:1 to 1:2.

The reactants are allowed to react under these conditions for asufficient time to allow upgrading reactions to occur. Preferably, theresidence time will be selected to allow the upgrading reactions tooccur selectively and to the fullest extent without having undesirableside reactions of coking or residue formation. Reactor residence timesmay be from 1 minute to 6 hours, preferably from 8 minutes to 2 hoursand most preferably from 10 to 40 minutes.

The present process includes the feature of maintaining an effectiveamount of metals, derived from the hydrocarbon undergoing upgrading, inthe reaction zone to catalyze desulfurization reactions. Since themetals removed from heavy oil will serve as catalyst for sulfur removal,it is important to maintain metal concentrations inside the reactor.With reference to the embodiment shown in FIG. 1, such requirement ismet by using a CSTR (continuous stirred tank reactor) type reactor. ForCSTR metals formed through metals removal reactions are well mixed withfeed stream and catalyze sulfur removal reactions, and therefore highremoval rate of both metal and sulfur can be achieved.

FIG. 2 shows another method of maintaining an effective amount of metalin the reaction zone. In this embodiment part of dreg stream whichcontains high concentration of metals is recycled back to maintainadequate metal concentration in the reactor. The metal concentrationinside the reactor can be controlled by adjusting recycle ratio. Suchrecycle strategy can also be used to control metal concentration when aCSTR is used. The dreg stream may either be withdrawn from anywhere itforms, for example from the reactor or from a high pressure separatorshown in FIG. 2.

Reaction Product Separation

After the reaction has progressed sufficiently, a single phase reactionproduct is withdrawn from the reaction zone, cooled, and separated intogas, effluent water, and upgraded hydrocarbon phases. This separation ispreferably done by cooling the stream and using one or more two-phaseseparators, three-phase separators, or other gas-oil-water separationdevice known in the art. However, any method of separation can be usedin accordance with the invention.

The composition of gaseous product obtained by treatment of the heavyhydrocarbons in accordance with the process of the present inventionwill depend on feed properties and typically comprises lighthydrocarbons, water vapor, acid gas (CO₂ and H₂S), methane and hydrogen.The effluent water may be used, reused or discarded. It may be recycledto e.g. the feed water tank, the feed water treatment system or to thereaction zone.

The upgraded hydrocarbon product, which is sometimes referred to as“syncrude” herein may be upgraded further or processed into otherhydrocarbon products using methods that are known in the hydrocarbonprocessing art.

The process of the present invention may be carried out either as acontinuous or semi-continuous process or a batch process or as acontinuous process. In the continuous process the entire system operateswith a feed stream of oil and a separate feed stream of water andreaches a steady state; whereby all the flow rates, temperatures,pressures, and composition of the inlet, outlet, and recycle streams donot vary appreciably with time. For continuous operations such as thoseshown in FIG. 1 and FIG. 2, oil feed will be heated up very quickly bysupercritical water, and a preferred means for achieving simultaneousremoval of metals, sulfur and nitrogen is using a reactor withbackmixing behavior or to recycle some of the reactor bottoms (dregstream) so that the metals removed from the feed oil will serve ascatalyst for sulfur removal reactions.

While not being bound to any theory of operation, it is believed that anumber of upgrading reactions are occurring simultaneously at thesupercritical water conditions used in the present process. In apreferred embodiment of the invention the major chemical/upgradingreactions are believed to be:

Thermal Cracking: C_(x)H_(y)→lighter hydrocarbons

Steam Reforming: C_(x)H_(y)+2xH₂O=xCO₂+(2x+y/2)H₂

Water-Gas-Shift: CO+H₂O=CO₂+H₂

Demetalization: C_(x)H_(y)Ni_(w)+H₂O/H₂→NiO/Ni(OH)₂+lighter hydrocarbons

Desulfurization: C_(x)H_(y)S_(z)+H₂O/H₂=H₂S+lighter hydrocarbons

The exact pathway may depend on the reactor operating conditions(temperature, pressure, O/W volume ratio), reactor design (mode ofcontact/mixing, sequence of heating), and the hydrocarbon feedstock.

The following Examples are illustrative of the present invention, butare not intended to limit the invention in any way beyond what iscontained in the claims which follow.

EXAMPLE 1 Experimental Process Description

A bomb reactor was loaded with a water and a heavy oil feed withAPI=12.8, which was a heavy crude oil which was diluted with a diluenthydrocarbon at a ratio of 5:1 (20 vol % of diluent). The reactor wasimmersed in a sand bath at reaction temperature so the temperatureinside the reactor was quickly raised to ˜400° C., typically in 3 to 5minutes. The reaction time was 30 minutes, and after reaction thereactor was quickly cooled down. The upgraded oil product and water werethen recovered from the bomb reactor.

The properties of the heavy crude feed were as follows: 12.8 API gravityat 60/60; 1329 CST viscosity @40° C.; 13.04 wt % MCRT; 3.54 wt % sulfur;0.56 wt % nitrogen; 3.05 mg KOH/gm acid number; 1.41 wt % water; 371 ppmVanadium; and 86 ppm Nickel.

After the super critical water treatment upgraded product (syncrude) hadthe following properties: 19.2 API gravity at 60/60; 3.15 wt % MCRT;0.54 wt % sulfur; 0.21 wt % nitrogen; 5.16 ppm Vanadium; and 1.09 ppmNickel. Substantial reductions in metals and sulfur were observed, withsimultaneous increase in the API gravity and a significant decrease inthe viscosity of the original crude oil feedstock.

EXAMPLE 2

The following procedure was performed using a continuous system. Thefeed oil was heated to 130° C. before entering a mixer. The heated crudewas injected into a stream of supercritical water at temperature of 400°C. The water to oil ratio (volume at room temperature) was 3:1. Theoil-supercritical water mixture was then injected into a reactor attemperature of 400° C. and pressure of 3400 psig. The upgraded product,which formed a homogeneous phase with supercritical water, was withdrawnfrom the top of the reactor and send to high pressure separator whichwas operated at the same pressure but lower temperature to achieveoil-water separation. The dreg stream was removed from reactor bottom.

The properties of the feed crude in Example 2 were as follows: 8 APIgravity at 60/60; 65689 CST viscosity @40° C.;. 15.7 wt % MCRT; 4.17 wt% sulfur; 0.68 wt % nitrogen; 5.8 mg KOH/gm acid number; 435 ppmVanadium; and 104 ppm Nickel.

After the super critical water treatment upgraded product (syncrude) hadthe following properties: 20.5 API gravity at 60/60; 10.9 CST viscosity@400° C., 2.2 wt % MCRT; 3.17 wt % sulfur; 0.29 wt % nitrogen; 40.9 ppmVanadium; and 5.9 ppm Nickel.

EXAMPLE 3

The procedure of Example 2 was repeated except that the properties ofthe feed crude were as follows: 8 API gravity at 60/60; 20,400 CSTviscosity @40° C.; 13 wt % MCRT; 5 wt % sulfur; 0.48 wt % nitrogen; 3.8mg KOH/gm acid number; 215 ppm Vanadium; and 80 ppm Nickel.

After the super critical water treatment upgraded product (syncrude) hadthe following properties: 18 API gravity at 60/60; 21 CST viscosity @40°C. 3 wt % MCRT; 4 wt % sulfur; 0.27 wt % nitrogen; 41 ppm Vanadium; and8 ppm Nickel.

For Examples 2 and 3, substantial reductions in metals, nitrogen andsulfur were observed, with simultaneous increase in the API gravity anda significant decrease in the viscosity of the original crude oilfeedstock.

There are numerous variations on the present invention which arepossible in light of the teachings,and supporting examples describedherein. It is therefore understood that within the scope of thefollowing claims, the invention may be practiced otherwise than asspecifically described or exemplified herein.

1. A process for removing metals, sulfur and nitrogen in the upgradingof hydrocarbons comprising: (a) mixing hydrocarbons containing metals,sulfur and nitrogen with a fluid comprising water that has been heatedto a temperature higher than its critical temperature in a mixing zoneto form a mixture; (b) passing the mixture to a reaction zone; (c)reacting the mixture in the reaction zone under supercritical waterconditions in the absence of externally added hydrogen for a residencetime sufficient to allow upgrading reactions to occur while maintainingan effective amount of metals, derived from the hydrocarbon undergoingupgrading, in the reaction zone to catalyze the upgrading reactions; and(d) recovering upgraded hydrocarbons having a lower concentration ofmetals, sulfur and nitrogen than the hydrocarbons of step (a).
 2. Aprocess according to claim 1, wherein the hydrocarbons are heavyhydrocarbons selected from the group consisting of whole heavy petroleumcrude oil, tar sand bitumen, heavy hydrocarbon fractions obtained fromcrude petroleum oils, heavy vacuum gas oils, vacuum residuum, petroleumtar, coal tar and their mixtures.
 3. A process according to claim 1,wherein the fluid comprising water enters the mixing zone at atemperature sufficiently higher than the critical temperature of waterso as to cause the resulting mixture to have a temperature higher thanthe critical temperature of water.
 4. A process according to claim 3,wherein the temperature of the fluid comprising water is from 400° C. to600° C.
 5. A process according to claim 1, wherein the hydrocarbons instep (a) are at a temperature of from 100° C. to 200° C.
 6. A processaccording to claim 1, wherein the supercritical water conditions includea temperature from 374° C. to 1000° C., a pressure from 3,205 psia to10,000 psia an oil/water volume ratio from 1:0.1 to 1:5 and where theresidence time is from 1 minute to 6 hours.
 7. A process according toclaim 1, wherein the supercritical water conditions include atemperature from 374° C. to 600° C., a pressure from 3,205 psia to 7,200psia, an oil/water volume ratio from 1:0.5 to 1:3 and where theresidence time is from 8 minutes to 2 hours.
 8. A process according toclaim 1, wherein the supercritical water conditions include atemperature from 374° C. to 400° C. a pressure from 3,205 psia to 4,000psia, an oil/water volume ratio from 1:1 to 1:2 and where the residencetime is from 10 to 40 minutes.
 9. A process according to claim 1,wherein the mixture in the reaction zone is reacted in the absence ofany externally supplied catalyst or promoter.
 10. A process according toclaim 1, further comprising the step of heating the mixture formed instep (a) to a temperature higher than the supercritical temperature ofwater before passing the mixture to the reaction zone.
 11. A process forremoving metals and sulfur in the upgrading of hydrocarbons comprising:(a) mixing hydrocarbons containing metals and sulfur with a fluidcomprising water having a temperature higher than the criticaltemperature of water in a mixing zone to form a mixture having atemperature higher than the critical temperature of water; (b) passingthe mixture to a reaction zone; (c) reacting the mixture in the reactionzone under supercritical water conditions in the absence of externallyadded hydrogen for a residence time sufficient to allow upgradingreactions including demetalation and desulfurization to occur whilemaintaining an effective amount of metals, derived from the hydrocarbonundergoing upgrading, in the reaction zone to catalyze desulfurizationreactions; and (d) recovering upgraded hydrocarbons having a lowerconcentration of metals and sulfur than the hydrocarbons of step (a) 12.A process according to claim 11, wherein the hydrocarbons are heavyhydrocarbons selected from the group consisting of whole heavy petroleumcrude oil, tar sand bitumen, heavy hydrocarbon fractions obtained fromcrude petroleum oils, heavy vacuum gas oils, vacuum residuum, petroleumtar, coal tar and their mixtures
 13. A process according to claim 11,wherein the fluid comprising water enters the mixing zone at atemperature sufficiently higher than the critical temperature of waterso as to cause the resulting mixture to have a temperature higher thanthe critical temperature of water.
 14. A process according to claim 13,wherein the temperature of the fluid comprising water is from 400° C. to600° C.
 15. A process according to claim 11, wherein the heavyhydrocarbons in step (a) are at a temperature of from 100° C. to 200° C.16. A process according to claim 10, wherein the supercritical waterconditions include a temperature from 374° C. to 1000° C., a pressurefrom 3,205 psia to 10,000 psia an oil/water volume ratio from 1:0.1 to1:5 and where the residence time is from 1 minute to 6 hours.
 17. Aprocess according to claim 10, wherein the supercritical waterconditions include a temperature from 374° C. to 600° C., a pressurefrom 3,205 psia to 7,200 psia, an oil/water volume ratio from 1:0.5 to1:3 and where the residence time is from 8 minutes to 2 hours.
 18. Aprocess according to claim 10, wherein the supercritical waterconditions include a temperature from 374° C. to 400° C., a pressurefrom 3,205 psia to 4,000 psia, an oil/water volume ratio from 1:1 to 1:2and where the residence time is from 10 to 40 minutes.
 19. A processaccording to claim 10, further comprising the step of heating themixture formed in step (a) to a temperature higher than the criticaltemperature of water before passing the mixture to the reaction zone.20. A process for removing metals and sulfur in the upgrading ofhydrocarbons comprising: (a) mixing hydrocarbons containing metals andsulfur with a fluid comprising water that has been heated to atemperature higher than its critical temperature in a mixing zone toform a mixture; (b) passing the mixture to a reaction zone; (c) reactingthe mixture in the reaction zone under supercritical water conditions inthe absence of externally added hydrogen for a residence time sufficientto allow upgrading reactions including demetalation and desulfurizationto occur while maintaining an effective amount of metals, derived fromthe hydrocarbon undergoing upgrading, in the reaction zone to catalyzedesulfurization reactions; (d) separating a dreg stream containingmetals from the reaction product; (e) passing at least a portion of thedreg stream to the reaction zone; and (g) recovering upgradedhydrocarbons having a lower concentration of metals and sulfur than thehydrocarbons of step (a).